Information on the physics of such a freezing process can be found in the German Patent DE-PS-1806741 and the European Patent Application EP-A-0 853238.
In professional circles, for example, such a known system of the applicant is employed, which is successfully marketed under the name "Leica EM HPF".TM. and described in the publication "LEICA EM HPF, High Pressure Freezer, 1.K.-LEICA EM HPF-E-6/94, Jun. 1994".
The "Leica EM HPF".TM. allows the vitrification of conventional samples under a pressure of ca. 2000 bar at a cooling rate of 10.sup.3 -10.sup.5 K/s. For the said appliance, the crucial cooling phase from ambient temperature to -100.degree. C. takes ca. 10 ms (cooling rate 10.sup.4 K/s) at the surface of the sample. Consequently, all samples with a thickness of ca. 200.mu.m are cooled to -100.degree. C. in ca. 50 ms.
The known cooling technology and the physical processes show clearly: Applying an infinitely high cooling rate to the surface of a biological sample only partially determines the rate of cooling in its centre. A sample of thickness 200 .mu.m, for example, exhibits a cooling rate in its centre of ca. 6000 K/s, regardless of whether an infinite cooling rate is employed at the surface or a cooling rate of ca. 10,000 K/s. The cooling rate is not determined by the pressure. By increasing the pressure, a lower cooling rate is sufficient for vitrification. Therefore, the cooling rate for the vitrification of biological samples is under standard pressure ca. 10.sup.5 - 10.sup.6 K/s, tinder 2000 bar, however, the cooling rate is only 10.sup.3- 10.sup.4 K/s, i.e., it is still possible to vitrify biological samples under high pressure using cooling rates a hundredfold lower.
The inventor referred in the article "A NEW CONCEPT AND MACHINE FOR HIGH PRESSURE FREEZING" from 15.3.1999, published in the internet under the address "www-mem.unibe.ch/.about. danis/abstract HPF", to these and further aspects of high-pressure freezing. He proposed increasing the pressure from 1 bar to 2000 bar within 10 ms by employing a compressed-air cylinder in place of the well-known very bulky and heavy equipment.
Pneumatic cylinders are already employed in a wide variety of applications. Using them to quickly build up high pressures, however, necessitates the use of large and heavy pumps.